Using current guidelines a considerable part of the patients, selected for cardiac resynchronization therapy (CRT) does not respond to the therapy. We hypothesized that mechanical discoordination (opposite strain within the left ventricular (LV) wall) predicts reversal of LV remodeling upon CRT better than mechanical dyssynchrony. Methods: MRI tagging images were acquired in CRT candidates (n=19) and in healthy control subjects (n=9). Circumferential strain (_cc) was determined in 160 regions. From _cc signals we derived 1) an index of mechanical discoordination (internal stretch fraction (ISF), defined as the ratio of stretch to shortening during ejection) and indices of mechanical dyssynchrony: the 10-90% width of 2a) time to onset of shortening, 2b) time to peak shortening and 2c) end systolic strain. LV end-diastolic volume (LVEDV), end-systolic volume (LVESV) and ejection fraction (LVEF) were determined before and after 3 months of CRT. Responders were defined as those patients where LVESV decreased by > 15%. Results: In responders (n=10), CRT increased LVEF and decreased LVEDV and LVESV (11±6%*, 21±16%* and 30±16%*, respectively) significantly more (*=p<0.05) than in the non-responders (1±6%, 3±4% and 5±10%, respectively). Among mechanical indices, only ISF was different between responders and non-responders (0.53±0.25* vs. 0.31±0.16, respectively). In patients with ISF>0.4 (n=10), LVESV decreased by 31±18%* versus 5±11% in patients with ISF<0.4. Conclusion: Mechanical discoordination, as estimated from ISF, is a better predictor of reverse remodeling after CRT than differences in time-to-onset and time-to-peak shortening. Discoordination rather than dyssynchrony appears to reflect the reserve contractile capacity that can be recruited by CRT.